1. Field of the Invention
The present invention relates to a panning control device, more particularly, to a panning control device for controlling an area of a display image on a display unit in a computer aided design system.
2. Description of the Related Art
Recently, a computer aided design (CAD) system using an engineering work station (EWS) has been developed and provided for various design work. Note, the CAD system is used in various fields, for example, the circuit design field, architectural design field, plant design field and the like, and in such a CAD system, a man-machine interface, by which a human operator communicates with the CAD system, is important, and thus a more advanced man-machine interface enabling an easy operation and a high speed operation is required.
Currently, a pointing device (for example, a mouse) is used as a man-machine interface in the CAD system, instead of a conventional keyboard, and graphic forms or drawings are easily described or edited by using the pointing device.
Note, in such a CAD system, when displaying a larger size graphic form than an image size of a display unit, or when displaying a whole shape of the graphic form on the display unit of the CAD system having a smaller image size of the display unit than the whole shape of the graphic form, the whole shape of the graphic form is reduced and displayed at the display unit of the CAD system. Nevertheless, it is difficult for an operator (or designer) to carry out a design process by using the reduced graphic form (or whole shape of the graphic form), and thus preferably a part of the graphic form having a larger scale is displayed at the display unit of the CAD system. Further, the CAD system should be able to freely change a display image on the display unit in accordance with the operator's requirements.
In a CAD system according to the prior art, to display a required part of a display image (or graphic form), first the operator points (pan-hits) at a specific position on a display image, and that image is then displayed at an image area of a display unit, by using a pointing device, and the display image is then changed so that the specific position (pan-hit position) pointed out by the pointing device is placed at the center of the image area of the display unit.
In the above prior art CAD system, however, only the display image displayed at the display unit (image area) is changed, and thereafter, the pan-hit position is placed at the center of the image area, and thus the operator cannot recognize the area of the following display image which has been changed after a panning operation (pan-hit operation) is completed. Accordingly, the pan-hit operation must be repeatedly carried out to obtain a display of a required area of the graphic form. Furthermore, when the pan-hit operation is carried out many times, a part of the graphic form currently displayed at the image area of the display unit cannot be immediately recognized by the operator, and in such a case, after displaying a whole shape of the graphic form by a reduction operation, an enlarging operation and then a pan-hit operation must be carried out.
As described above, in the prior art CAD system, a problem arises in that the labour effectivity thereof cannot be increased because a required part of the display image cannot be easily displayed at the image area of the display unit.